Linear alpha-olefins, which are important materials used as comonomers, cleaners, lubricants, plasticizers and the like, are commercially widely used, and particularly, 1-hexene and 1-octene are used a lot as comonomers for controlling the density of polyethylene when preparing linear low-density polyethylene (LLDPE).
In the existing preparation process of LLDPE, ethylene is copolymerized with alpha-olefin comononers, such as 1-hexene and 1-octene, so as to form branches in the polymer backbone to control the density.
Thus, there is a problem in that the cost of comonomers occupies a large part of production cost in the preparation of LLPDE having high comonomer content. There have been various attempts to solve the problem.
And, since alpha-olefins have various different application fields or market sizes according to the kind, a technology of selectively producing a specific olefin is commercially very important, and recently, a lot of studies are being progressed on the chromium catalyst technology for preparing 1-hexene or 1-octene with high selectivity through selective ethylene oligomerization.
The existing commercial preparation methods of 1-hexene or 1-octene include the SHOP process of Shell Chemical, the Ziegler process of Chevron Philips, and the like, whereby C4-20 alpha-olefins with a wide distribution can be produced.
As a catalyst for trimerization of ethylene, a chromium-based catalyst using a ligand of the General Formula (R1)(R2)X—Y—X(R3)(R4) has been suggested. Wherein, X is phosphorous, arsenic or antimony, Y is a linking group such as —N(R5)—, and at least one of R1, R2, R3 and R4 has a polar or electron donating substituent.
And, as a ligand that exhibits catalytic activity to 1-hexene under catalytic conditions, studies have been progressed on (o-ethylphenyl)2PN(Me)P(o-ethylphenyl)2, which does not have a polar substituent on at least one of R1, R2, R3 and R4 (Chem. Commun., 2002, 858).
However, regarding the above explained ligand containing a heteroatom of the prior art, there is continued demand for consistently continued multimerization activity and high selectivity when preparing 1-octene or 1-hexene.